There remains a critical need to develop new safe and effective antiviral agents active against the human pathogens, herpes simplex virus (HSV) and human cytomegalovirus (CMV). The broad long term objectives of this project are to identify, characterize, overexpress, and exploit novel targets for such drugs. The project takes a combined approach to drug development in which advantageous elements of traditional drug development approaches are combined with rational design. Novel drug targets are identified using resistance to previously existing drugs, the drug targets are characterized molecularly and overexpressed, and with the information gained used to design and screen new compounds. The first specific aim is to design novel drugs that target a well-established target, the HSV DNA polymerase (Pol), whose gene was first identified via drug resistance mutations. This enzyme interacts with a protein, UL42, which is required for polymerase processivity. Peptides derived from the portions of each protein involved in the interaction will be tested for their ability to disrupt Pol-UL42 complex formation and replicative activities. RNA molecules that bind to these portions of the protein will be derived using a new method and similarly tested. These compounds will be modified to generate potent inhibitors of HSV replication. The second specific aim begins with a novel drug target that is yet undefined, the CMV gene product that contributes to ganciclovir phosphorylation. The existence of this drug target has been inferred from studies of ganciclovir-resistant CMV mutants. The gene encoding this target will be mapped, cloned, characterized molecularly, and overexpressed. The information and reagents developed will be used to design and screen new inhibitors of CMV replication. The third specific aim begins with drugs for whom targets have not yet been assigned. These include drugs with activity against HSV, CMV, or both and drugs that potentiate the action of acyclovir against these viruses. Mutants resistant to these drugs will be isolated. The genes encoding each novel drug target will be mapped, cloned, characterized, molecularly, and overexpressed. The information and reagents developed will be used to design and screen new inhibitors of CMV replication.